diff --git a/HISTORY.md b/HISTORY.md
index 0710571..d2c440c 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,6 +2,7 @@ unreleased
 ==================
 
   * remove `ServerResponse.headersSent` support check
+  * remove setImmediate support check
   * remove unnecessary devDependency `safe-buffer`
   * remove `unpipe` package and use native `unpipe()` method
   * remove unnecessary devDependency `readable-stream`
diff --git a/index.js b/index.js
index 7d24afb..144ef35 100644
--- a/index.js
+++ b/index.js
@@ -26,10 +26,6 @@ var statuses = require('statuses')
 var DOUBLE_SPACE_REGEXP = /\x20{2}/g
 var NEWLINE_REGEXP = /\n/g
 
-/* istanbul ignore next */
-var defer = typeof setImmediate === 'function'
-  ? setImmediate
-  : function (fn) { process.nextTick(fn.bind.apply(fn, arguments)) }
 var isFinished = onFinished.isFinished
 
 /**
@@ -118,7 +114,7 @@ function finalhandler (req, res, options) {
 
     // schedule onerror callback
     if (err && onerror) {
-      defer(onerror, err, req, res)
+      setImmediate(onerror, err, req, res)
     }
 
     // cannot actually respond